System and Method to Improve Operation of Hydraulic Pump for Subsea Service

ABSTRACT

The operating performance and reliability of a pump, e.g. a hydraulic pump, can be significantly improved by incorporating an actively controlled positive displacement control valve in fluid communication with a fixed displacement pump, supply fluid line, and return fluid line. In use, the pump may be used to move fluid from the suction side to the discharge side of the pump, including fully opening the suction circuit to the pump cylinder and fully closing the pump discharge circuit during a pump suction stroke, fully closing the suction circuit and fully opening the pump discharge circuit to a downstream circuit during a pump discharge stroke, and allowing fluid to be pumped without the fluid passing through a valve spring loaded check valve.

CLAIM TO PRIORITY

This application claims the benefit of priority under 35 U.S.C. §119(e)from U.S. Provisional Patent Application No. 61/762,743 entitled “Methodto Improve Operation of Hydraulic Pump for Subsea Service”, filed Feb.8, 2013, which is incorporated herein in its entirety by this reference.

FIELD OF THE INVENTION

The operating performance and reliability of a pump, e.g. a hydraulicpump, can be significantly improved by incorporating “PositiveDisplacement Control Valve” technology as shown in the following figuresand description.

BACKGROUND OF THE INVENTION

A single cycle of a reciprocating piston pump typically has twocomponents: a suction stroke and a discharge stroke. During the pumpsuction stroke, fluid flows through a pump suction port into the pumpcylinder. The movement of the pump piston usually draws the fluid from alocal reservoir or supply conduit. With the pump discharge stroke, thefluid within the pump cylinder is pushed out of the pump by the pumppiston; exiting through a pump discharge port where it is routed to adifferent location like, for example, a pipeline or tank.

In the simplest terms, a pump moves fluid from the suction side to thedischarge side of the pump, and, in doing so, adds energy to thedisplaced fluid. As a secondary effect of moving the fluid through thepump, the pump generally reduces pressure on the suction side whileincreasing pressure on the discharge side of the pump.

A pump must be driven by a mechanism that supplies the energy to movethe pump piston. A simple hydraulic driven intensifier pump is reallytwo back-to-back hydraulic cylinders. One hydraulic cylinder contains apiston which is cyclically reciprocated by a separate hydraulic powerunit and directional control valve. This “drive cylinder” ismechanically linked to, thereby also reciprocating, a second piston in a“pumping cylinder.”

Fluid must flow through the pump in only one direction; from the suctionport to the discharge port. In conventional pumps, check valves are usedin the suction and discharge lines to/from the pump to ensure that theflow is uni-directional. These check valves are, in general, springloaded, poppet-and-seat type valves that only allow flow through thevalve in one direction. A pressure differential in the “flow” directionmoves the poppet off the seat, compressing the spring, and opening aflow path through the check valve. When this pressure differentialsufficiently decreases, the spring forces the poppet against the seat,closing off the reverse flow path through the check valve. Byautomatically responding to internal pressure differentials, checkvalves provide automatic passive operation requiring no additionalexternal controls. Check valves provide a simple and effective solutionfor controlling flow direction in conventional pumping applications.However, as will be explained below there are several disadvantages withusing check valves in the unconventional applications as we have indeepwater subsea oilfield service.

Check valves are sensitive to solid contaminants in the fluid beingpumped. The geometry of the poppet and seat arrangement in a check valvetends to trap contaminants between the poppet and seat preventing thecheck valve from shutting off flow in the reverse “no-flow” direction.This is a major limitation of check valves in any service involvingcontaminated liquids.

One growing unconventional subsea application requires the use of pumpsto reduce the pressure in a subsea piping system that has been blockeddue to a hydrocarbon “ice” (methane hydrate or methane clathrate) plugthat can form under certain conditions. Reducing the pressure around theplug causes the ice to melt, allowing the piping circuit to be restoredto normal operation. The lower the pressure that can be achieved by thepump, the faster the ice plug will melt.

Another application includes the use of subsea pumps for deliveringvarious treating chemicals into the subsea well or production pipingsystem. In most of these cases, the volume of chemical delivered must becontrolled and measured. So the subsea pump becomes not only a fluidpumping device, but also a fluid volumetric metering device; hence thename “metering pump”. Metering pumps are commonly used for conventionalnon-subsea applications. Indeed, the conventional pump depicted in theoriginal disclosure is commonly used for chemical metering applicationsfor conventional non-subsea applications.

There are several limitations to using conventional pump check valves incertain applications. The oilfield piping circuit containing the iceplug can contain significant solid contaminants that can become lodgedin the pump check valves resulting in pumping system failure. Plugs cansometimes be composed of hydrate mixed with other materials common incrude oil that can plug lines, like asphaltenes, waxes or polymerformations. The pressure in the piping circuit can only be reduced tothe opening pressure of the pump suction check valve; increasing thetime that it takes to melt the ice plug. The basic design of areciprocating pump in gas service is limited by the “pressure ratio”which is an engineering relationship between pump stroke volume andoperating pressure of the pump check valves. There is also a significantlimitation to using conventional check valves in unconventional subseapumping applications.

After some period of continued production from a subsea oilfield, thepressure in the hydrocarbon reservoir, and downstream piping system,decreases to a level below which the treating chemical will actuallyfree-flow or “auto-siphon” from the storage reservoir through the pumpcheck valves and into the subsea piping system bypassing the capabilityand purpose of the metering pump to control the volume of chemical used.Indeed the chemical metering pump discharge pressure in a subseaproduction system may vary from 15,000 psi to −4000 psi relative to thepump suction pressure over the production life of a deepwater oilfield.

One possible way of mitigating this auto-siphoning effect is tointroduce an in-line relief valve or back-pressure valve downstream ofthe pump. However this type of device is subject to high mechanicalstresses, sensitive to contamination, and must be adjusted for changingconditions over the field life.

FIGURES

The figures supplied herein disclose various embodiments of the claimedinvention.

FIG. 1 is a block diagram of an exemplary embodiment of a pump; and

FIG. 2 is a block diagram of an exemplary embodiment of a systemincorporating a pump.

DESCRIPTION OF VARIOUS EMBODIMENTS

Referring generally to FIG. 1 and FIG. 2, the operating performance andreliability of a subsea pump can be improved by incorporating thetechnology as shown in the following figures and description. In itsembodiments, the disclosed system 1 (FIG. 2) may be technology used for,e.g., subsea chemical injection pumping systems and presents animprovement in subsea pumps used for hydrate remediation work.

As will be apparent to those of ordinary skill in subsea pump arts, inthe various embodiments system 1 may be used to help preventauto-siphoning of fluids through pump when operating in sub-ambientdischarge conditions; provide positive displacement operation allowingmetered flow of fluids independent of suction or discharge conditions;eliminate lower reliability spring-loaded check valves; provide fullflow bores through pump suction and discharge to improve contaminationresistance; allow lower suction pressure, which is an advantage topipeline scavenging operations such as a subsea hydrate remediationoperation; and provide a pump design that is not limited by compressionratio.

Referring to FIG. 1, in an embodiment, system 1 (FIG. 2) comprisessubsea pump 2 useful for subsea service. Subsea pump 2 comprises fixeddisplacement pump 10, inlet valve 21 in fluid communication with fixeddisplacement pump 10; supply fluid line 25 in fluid communication withinlet valve 21; return fluid line 26 in fluid communication with inletvalve 21; outlet valve 23 in fluid communication with fixed displacementpump 10; suction line 32 in fluid communication with outlet valve 23;and discharge line 36 in fluid communication with outlet valve 23.

In preferred embodiments fixed displacement pump 10 comprises drivecylinder 11, further comprising drive piston 12 which is cyclicallyreciprocated by a separate hydraulic power unit and directional controlvalve (not shown in the figures) and pumping cylinder 13, furthercomprising pumping piston 14 which is cyclically reciprocated by theseparate hydraulic power unit and directional control valve.

However, fixed displacement pump 10 may be driven hydraulically,electrically, and/or mechanically. Additionally, valves 20,30 may becontrolled actively and/or passively and may further be operatedhydraulically, electrically, and/or mechanically.

Drive cylinder 11 may be operatively linked to pumping cylinder 13. Insome embodiments, drive cylinder 11 is larger than pumping cylinder 13.

Referring additionally to FIG. 2, system 1 may further comprise activecontroller 40 operatively connected to the fixed displacement pump 10and valves 20,30. Active controller 40 may further compriseinstrumentation 41 suitable for feedback, such as a position sensor, apressure sensor, a temperature sensor, a flow meter, a sensor configuredto aid in fluid qualitative analysis, or the like, or a combinationthereof.

In certain embodiments, positive displacement control valve 30 may beconfigured using very robust, contamination resistant, hardened metalseal elements similar to those used in subsea oilfield gate valves andblowout preventer (BOP) control systems. This type of seal element iscapable of shearing even large solid contaminants that may enterpositive displacement control valve 30 when, for example, pumpingliquids from a hydrocarbon pipeline.

In the operation of exemplary embodiments, operation of subsea pump 2may be improved for a subsea service by using the disclosed system whichcan be used without requiring spring loaded check valves. In general,the method includes the use an actively controlled positive displacementcontrol valve 30 in the pumping circuit instead of conventional checkvalves, as described above. In its embodiments, this method allows fluidto be pumped without passing through a check valve, eliminating manylimitations of a pump that uses this type of valve. Subsea pump 2, whichis more contamination resistant and inherently more reliable, is capableof reducing the suction pressure without the limitation of overcomingthe spring force in the suction check valve. Additionally, the pumpdesign is no longer as limited by compression ratio as prior art pumps.

Platform mounted chemical metering pumps are commonly used to injectchemicals into subsea wells and flowlines via long umbilical tubesextending to the subsea injection point. However, the deepwater subseaapplications, largely in the Gulf of Mexico, have only recently maturedto the point where the subsea production pressures are lower than theminimum possible controllable delivery pressure of a topsides meteringpump. There is starting to be significant volumes of chemical beinginadvertently injected into subsea wells and flowlines from theseplatforms, and this problem will increase in the coming years. Even inthis topsides pump application, positive displacement control valve 30would be an improvement over conventional technology.

Subsea services may comprise preventing auto-siphoning of the fluidthrough a chemical metering pump in applications where the dischargepressure is lower than the suction pressure. One advantage of thedisclosed method is to prevent auto-siphoning of fluid through achemical metering pump in applications where the discharge pressure islower than the suction pressure. Additionally, subsea services maycomprise using positive displacement control valve 30 where a pressureof a subsea production is lower than the minimum possible controllabledelivery pressure of a topsides metering pump. Further, subsea servicesmay include chemical injection into a fluid flowline, chemical metering,hydraulic fluid supply and power, pressure management, integritytesting, blockage remediation, or the like, or a combination thereof.

Subsea pump 2 is typically disposed subsea. As described herein,positive displacement control valve 30 is disposed in the pumpingcircuit and comprises two internal valve circuits 31,33 that act toalternately open and close the pump suction and discharge circuits insync with the suction and discharge pump strokes.

Design of subsea pump 2 may be substantially not limited by compressionratio. Moreover, positive displacement control valve 30 may beconfigured to perform where conditions at inlet valve 21 or outlet valve23 are above or below ambient pressures in any combination. Positivedisplacement control valve 30 may be operated hydraulically,electrically, or mechanically such as through a linkage to the pumpdrive mechanism.

Subsea pump 2 may be used to move fluid from the suction side, e.g.suction valves 31-32, to the discharge side of subsea pump 2, e.g.discharge valves 33-34. In an embodiment this process comprises fullyopening the suction circuit to pump cylinders 11,13 and fully closingthe pump discharge circuit during a pump suction stroke and fullyclosing the suction circuit, e.g. 25, and fully opening the pumpdischarge circuit, e.g. 26, to a downstream circuit during a pumpdischarge stroke.

During the pump suction stroke, fluid may be allowed to flow throughpump suction port 35 into pump cylinder 13, drawing the fluid from localreservoir 100 or supply conduit by the movement of pump piston 14.Additionally, during the pump discharge stroke, fluid may be pushedwithin pump cylinder 13 out of subsea pump 2 by pump piston 13, allowingthe fluid to exit through pump discharge port 36.

Fluid may then be pumped without the fluid passing through a valvespring loaded check valve. Exiting fluid may be routed to a differentlocation such as pipeline 110 or a tank or the like.

In certain operations, the operation of positive displacement controlvalve 30 may be synchronized with the pump operation. There are variousmethods of synchronizing the operation of positive displacement controlvalve 30 with the pump operation. For example, positive displacementcontrol valve 30 may be operated hydraulically, electrically, or evenmechanically through a linkage to the pump drive mechanism. Theimprovements realized from the use of such positive displacement controlvalve 30 in pump 2 in subsea applications are independent of theparticular method used to synchronize the operation with pump 2.

In certain embodiments, suction pressure may be reduced without needingto overcome a spring force in the suction check valve.

The foregoing disclosure and description of the inventions areillustrative and explanatory. Various changes in the size, shape, andmaterials, as well as in the details of the illustrative constructionand/or a illustrative method may be made without departing from thespirit of the invention.

1. A system for pumping fluids subsea, comprising: a. a fixeddisplacement pump, the fixed displacement pump comprising: i. a drivecylinder, comprising a drive piston configured to be cyclicallyreciprocated by a separate hydraulic power unit and directional controlvalve; and ii. a pumping cylinder, comprising a pumping pistonconfigured to be cyclically reciprocated by the separate hydraulic powerunit and directional control valve, the drive cylinder operativelylinked to the pumping cylinder; b. an inlet valve in fluid communicationwith the fixed displacement pump; c. a supply fluid line in fluidcommunication with the inlet valve; d. an outlet valve in fluidcommunication with the fixed displacement pump; e. a return fluid linein fluid communication with the outlet valve; f. an actively controlledpositive displacement control valve in fluid communication with thefixed displacement pump, the supply fluid line, and the return fluidline; g. a suction line port in fluid communication with the positivedisplacement control valve; and h. a discharge line port in fluidcommunication with the positive displacement control valve.
 2. Thesystem of claim 1, wherein the fixed displacement pump may be drivenhydraulically, electrically, and/or mechanically.
 3. The system of claim1, wherein the inlet valve and the positive displacement control valvemay be controlled actively and/or passively and may further be operatedhydraulically, electrically, and/or mechanically.
 4. The system of claim1, further comprising an active controller operatively connected to thepump, the inlet valve, and the positive displacement control valve. 5.The system of claim 4, wherein the active controller further comprisesinstrumentation adapted for providing feedback to the active controller.6. The system of claim 5, wherein the instrumentation further comprisesa position sensor, a pressure sensor, a temperature sensor, a flowmeter, or a sensor configured to aid in fluid qualitative analysis. 7.The system of claim 4, wherein the positive displacement control valvecomprises contamination resistant, hardened metal seal elements.
 8. Thesystem of claim 1, wherein the drive cylinder is larger than the pumpingcylinder.
 9. A method of improving operation of a subsea pump for asubsea service, comprising: a. disposing a pump subsea, the comprising:i. a fixed displacement pump, the fixed displacement pump comprising: 1.a drive cylinder, comprising a drive piston configured to be cyclicallyreciprocated by a separate hydraulic power unit and directional controlvalve; and
 2. a pumping cylinder, comprising a pumping piston configuredto be cyclically reciprocated by the separate hydraulic power unit anddirectional control valve, the drive cylinder operatively linked to thepumping cylinder; ii. an inlet valve in fluid communication with thefixed displacement pump; iii. a supply fluid line in fluid communicationwith the inlet valve; iv. an outlet valve in fluid communication withthe fixed displacement pump; v. a return fluid line in fluidcommunication with the outlet valve; vi. an actively controlled positivedisplacement control valve in fluid communication with the fixeddisplacement pump, the supply fluid line, and the return fluid line;vii. a suction line port in fluid communication with the positivedisplacement control valve; and viii. a discharge line port in fluidcommunication with the positive displacement control valve; and b. usingthe pump to move fluid from the suction side to the discharge side ofthe pump, moving comprising: i. during a pump suction stroke, fullyopening the suction circuit to the pump cylinder and fully closing thepump discharge circuit; ii. during a pump discharge stroke, fullyclosing the suction circuit and fully opening the pump discharge circuitto a downstream circuit; and iii. allowing fluid to be pumped withoutthe fluid passing through a valve spring loaded check valve.
 10. Themethod of claim 9, further comprising reducing suction pressure withoutneeding to overcome a spring force in a suction check valve.
 11. Themethod of claim 9, further comprising not limiting the pump design bycompression ratio.
 12. The method of claim 9, wherein the subsea servicecomprises preventing auto-siphoning of the fluid through a chemicalmetering pump in applications where discharge pressure is lower thansuction pressure.
 13. The method of claim 9, further comprisingsynchronizing the operation of the positive displacement control valvewith the pump operation.
 14. The method of claim 9, wherein the positivedisplacement control valve is configured to perform where conditions atthe inlet valve or outlet valve are above or below ambient pressures inany combination.
 15. The method of claim 9, further comprising operatingthe positive displacement control valve hydraulically, electrically, ormechanically through a linkage to the pump drive mechanism.
 16. Themethod of claim 9, wherein the subsea service comprises using thepositive displacement control valve where a pressure of a subseaproduction is lower than the minimum possible controllable deliverypressure of a topsides metering pump.
 17. The method of claim 9, whereinthe subsea service comprises at least one of chemical injection into afluid flowline, chemical metering, hydraulic fluid supply and power,pressure management, integrity testing, or blockage remediation.
 18. Themethod of claim 9, wherein: a. during the pump suction stroke, allowingfluid to flow through the pump suction port into the pump cylinder anddrawing the fluid from a local reservoir or supply conduit by themovement of the pump piston; and b. during the pump discharge stroke,pushing the fluid within the pump cylinder out of the pump by the pumppiston and allowing the fluid to exit through the pump discharge port.19. The method of claim 9, wherein exiting fluid it is routed to apipeline or tank.